mavttsd: a pronunciation dictionary, so she says the names right (V-458)

piper reads a Russian sentence with a Russian voice, and a Latin service id
inside it comes out spelled, mangled or read as if it were a Russian word:
"Vikunja", "SearXNG", "homesrv". The lever available is the text, so the
dictionary maps a name to how it should be spelled for the voice to say it,
and mavttsd applies it at the last edge before piper — every caller's text
passes through that one point, and nothing upstream has to know how a name
sounds.

Data, not code. deploy/tts-lexicon.json ships 29 names; adding one needs a
restart of mavttsd and no rebuild of the daemon that produced the text. Off
unless -lexicon is set, like every other optional capability, and a path that
is set and unreadable stops startup — saying names wrong in silence is the
failure it exists to remove.

Two details worth keeping: the alternation is sorted longest-first, or "Home
Assistant" reads as "Хоум Assistant"; and the boundaries are written out
rather than left to \b, which is ASCII-only and never fires next to a
Cyrillic letter.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/tts/lexicon_test.go

@@ -0,0 +1,85 @@
+package tts
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLexiconRewritesNames(t *testing.T) {
+	lex := NewLexicon(map[string]string{
+		"Vikunja":        "Викунья",
+		"Home Assistant": "Хоум Ассистент",
+		"Home":           "Хоум",
+		"GPU":            "джи-пи-ю",
+	})
+	for _, tc := range []struct{ in, want string }{
+		{"задача в Vikunja готова", "задача в Викунья готова"},
+		// Case-insensitive: the router and the model both change the case of a
+		// name on the way through.
+		{"открой vikunja.", "открой Викунья."},
+		// Longest first, or "Home Assistant" is read as "Хоум Assistant".
+		{"Home Assistant не отвечает", "Хоум Ассистент не отвечает"},
+		// Two names in a row share the space between them, which one pass
+		// would consume.
+		{"GPU GPU", "джи-пи-ю джи-пи-ю"},
+		// Not a word boundary: a name inside a longer token is left alone.
+		{"vikunjaless", "vikunjaless"},
+		{"ничего не совпало", "ничего не совпало"},
+		{"", ""},
+	} {
+		if got := lex.Apply(tc.in); got != tc.want {
+			t.Errorf("Apply(%q) = %q, want %q", tc.in, got, tc.want)
+		}
+	}
+}
+
+// The zero value and an unconfigured path rewrite nothing, so a daemon with no
+// dictionary behaves as it did before this existed.
+func TestLexiconOffByDefault(t *testing.T) {
+	var zero *Lexicon
+	if got := zero.Apply("Vikunja"); got != "Vikunja" {
+		t.Errorf("nil lexicon rewrote %q", got)
+	}
+	lex, err := LoadLexicon("")
+	if err != nil {
+		t.Fatalf("LoadLexicon(\"\"): %v", err)
+	}
+	if lex.Size() != 0 || lex.Apply("Vikunja") != "Vikunja" {
+		t.Errorf("empty path produced a live lexicon of %d names", lex.Size())
+	}
+}
+
+// A path he set and that cannot be read is a startup failure. Saying names
+// wrong in silence is what the dictionary exists to stop.
+func TestLexiconLoadErrors(t *testing.T) {
+	if _, err := LoadLexicon(filepath.Join(t.TempDir(), "nope.json")); err == nil {
+		t.Error("a missing dictionary must be an error")
+	}
+	bad := filepath.Join(t.TempDir(), "bad.json")
+	if err := os.WriteFile(bad, []byte("{not json"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := LoadLexicon(bad); err == nil {
+		t.Error("an unparseable dictionary must be an error")
+	}
+}
+
+func TestLexiconRoundTripsAFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "lex.json")
+	if err := os.WriteFile(path, []byte(`{"Praxis":"Праксис","  ":"skipped","Nexus":""}`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	lex, err := LoadLexicon(path)
+	if err != nil {
+		t.Fatalf("LoadLexicon: %v", err)
+	}
+	// Blank names and blank spellings are dropped: an entry that says nothing
+	// would delete the word it matched.
+	if lex.Size() != 1 {
+		t.Fatalf("Size = %d, want 1", lex.Size())
+	}
+	if got := lex.Apply("Praxis молчит"); got != "Праксис молчит" {
+		t.Errorf("Apply = %q", got)
+	}
+}